1. Field of the Invention
The present invention relates to a paging method in a mobile communication system based on Internet Protocol (hereinafter referred to as IP); the mobile communication system; a server, a base station, and a mobile station constituting this system; and a paging program executed in the server.
2. Related Background Art
A second generation cordless telephone system referred to as PHS (Personal Handyphone System) has been known (ARIB RCRSTD-28 Version 3.2: Second Generation Cordless Telephone System Standard). An incoming packet addressed to the mobile station in this system is received, a server refers to the location information of the destination mobile station in a PHS service control station, and a paging control packet is broadcasted in a paging area including a cell where the mobile station locates in. Also, using PCH (paging channel), paging control packet is broadcasted from the base station to the mobile station.
On the other hand, a digital car phone system referred to as PDC (Personal Digital Cellular) has been known (ARIB RCR STD-27H: Digital Car Phone System Standard). An incoming packet addressed to the mobile station in this system is received, a server refers to the location information of the mobile station in HLR (home location register) in the case of users within a home network or in GLR (gateway location register) in the case of roaming users, and a paging control packet is broadcasted for a plurality of base stations within a paging area in which the mobile station has registered its location information, using PCH (paging channel), paging control packet is broadcasted from the base station to the mobile station.
Meanwhile, a mobile IP technique has been known. The outline of mobile IP will now be explained with reference to FIG. 9. It is assumed that a terminal 91 is about to communicate with a portable terminal (mobile host, hereinafter referred to as MH) 98 such as cellular phone or mobile terminal. Suppose that the MH 98 is in the cell of a foreign agent (hereinafter referred to as FA) 95. The terminal 91 transmits a packet 92 addressed to the MH 98.
Thus transmitted packet 92 is transferred to a home agent (hereinafter referred to as HA) 93, where an address X corresponding to the FA 95 whose cell the MH 98 located in is added to the transferred packet, to generate a packet 94. Thereafter, the packet 94 is transferred to the FA 95. The FA 95 eliminates the added IP address X, and transfers the resulting packet 97 to the MH 98. As a consequence, the terminal 91 and the MH 98 communicate with each other.
Suppose that the MH 98 moves from the cell of the FA 95 to the cell of another FA 96. Thus moved MH 98 reports its own IP address and the IP address Y of FA 96 to the HA 93 and, at the same time, its own IP address to the FA 96. In the subsequent communication addressed to the MH 98, the HA 93 adds the IP address Y of the FA 96 to the packet, thus generating a packet 99. As a consequence, MH 98 can continue communicating even after the MH 98 moves from the cell of the FA 95 to the cell of the FA 96.
However, the above-mentioned techniques about PHS and PDC have not been concerned with the implementation of IP, and may not achieve high compatibility with the Internet, thus failing to consider their application to future mobile communication systems using IP networks.
Also, in mobile IP since there is only one FA whose cell an MH located in, hand-over is executed every time the MH moves between cells. Namely, even if the MH is in the idle state, it must register its location information to the HA and the FA whose cell the MH moved into when transiting between cells. This increases the control traffic at the time of registering the location information, and the increase may worsen channel efficiency and enlarge battery consumption, thus being unsuitable for high-speed, large-capacity multimedia mobile communication systems using IP networks for covering a large area.